Recently, an image forming apparatus of an electrophotographic scheme such as a laser printer, a digital copier, or a laser facsimile is equipped with a post-processing device (finisher) which staples or sorts a bunch of papers, as disclosed in, for example, JP-A 2007-76893.
In the finisher, a reciprocating motion of an assist arm (an ejector) is carried out by, for example, a reciprocal motion of a belt (hereinafter, referred to as “an eject belt”) to which the ejector is fixed, as shown in JP-A 2007-76893.
In order to increase a throughput of a stapling processing or sorting processing performed repeatedly, it is required to increase a moving speed of the ejector in the returning path as well as in the going path. In addition, the ejector is required to stop at the home position accurately and further surely. In order to satisfy these requirements, a torsional coil spring with a large elastic force it is require is used for the movement of the returning path.
Meanwhile, a protrusion is provided on a predetermined position of the eject belt. The protrusion collides with a belt stopper fixed outside the eject belt, thereby stopping the movement of the eject belt in the returning direction. The stop position of the eject belt is adjusted such that the ejector stops at the home position.
Due to the large elastic force of the torsional coil spring, the eject belt accelerates considerably right before the protrusions thereof collide with the belt stopper.
As a result, conventionally, the protrusions on the eject belt collide with the belt stopper for stopping in an impact manner, thereby generating an impact sound. When the stapling processing or the sorting processing is performed repeatedly, the impact sound is also generated repeatedly.